Here, a transmission refers in particular to a multi-ratio transmission in which a multiplicity of gear ratios, between the input shaft and the output shaft can be selected, preferably automatically, by shift elements. The shift elements are in this case for example clutches or brakes. Such transmissions are used in particular in motor vehicles for the purposes of suitably adapting the rotational speed and torque output characteristics of the drive unit to the driving resistances of the vehicle.
FIG. 20 of the patent application WO 2006/015845 A1 discloses a multi-ratio automatic transmission having a drive shaft, an output shaft, an upstream gear set, a main gear set and at least six shift elements, such a multi-ratio automatic transmission makes it possible to realize at least eight forward gear ratios that can be selected without performing compound shifts. The main gear set is formed by a Simpson gear set which is composed of two individual planetary gear sets. For this purpose, the sun gears of the two planetary gear sets are permanently connected and thereby form a first coupling shaft. The carrier of the first planetary gear set is permanently connected to the ring gear of the second planetary gear set, whereby a second coupling shaft is formed. Here, one of the two individual planetary gear sets is formed as a stepped planetary gear set, the planet gears of which have two different effective diameters. The output shaft is directly connected to the second coupling shaft.
The applicant's patent application DE 10 2013 225 208.0, which does not constitute a prior publication, describes in FIG. 6, a transmission having a first planetary gear set and a second planetary gear set, which are in the form of Simpson gear sets. An output shaft is permanently connected to the second coupling shaft. The transmission furthermore has an electric machine with a rotatable rotor and with a rotationally fixed stator, the rotor being connected to a sun gear of an additional planetary gear set, and the carrier and ring gear of the additional planetary gear set being connected to two shafts of the Simpson gear set. The transmission has a total of four forward gear ratios between the input shaft and the output shaft.
Both of the above mentioned transmissions have a total of three planetary gear sets, and thus require a high level of outlay in terms of construction and a suitably large installation space. Furthermore, the additional planetary gear set impairs the efficiency of the transmission.